In situ observation of chemistry in Rydberg molecules within a coherent solvent

TL;DR

This study observes how Rydberg molecules interact with a Bose-Einstein condensate, revealing their internal electronic state changes and dynamics through in-situ optical imaging, advancing understanding of ultra-cold molecular chemistry.

Contribution

It introduces a method to visualize and analyze the internal electronic state conversions of Rydberg molecules within a BEC using optical microscopy.

Findings

Rydberg molecules induce observable signatures in the BEC.

Electronic state rapidly converts to a complex 'trilobite' state.

Molecules decelerate significantly in the medium, contrary to expectations.

Abstract

We often infer the state of systems in nature indirectly, for example, in high-energy physics by the interaction of particles with an ambient medium. We adapt this principle to energies $9$ orders of magnitude smaller, to classify the final state of exotic molecules after internal conversion of their electronic state, through their interaction with an ambient quantum fluid, a Bose-Einstein condensate (BEC). The BEC is the ground-state of a million bosonic atoms near zero temperature, and a single embedded ultra-long range Rydberg molecule can coherently excite waves in this fluid, which carry telltale signatures of its dynamics. Bond lengths exceeding a micrometer allow us to observe the molecular fingerprint on the BEC in-situ, via optical microscopy. Interpreting images in comparison with simulations strongly suggests that the molecular electronic state rapidly converts from the initially excited S and D orbitals to a much more complex molecular state (called "trilobite''), marked by a maximally localized electron. This internal conversion liberates energy, such that one expects final-state particles to move rapidly through the medium, which is however ruled out by comparing experiment and simulations. The molecule thus must strongly decelerate in the medium, for which we propose a plausible mechanism. Our experiment demonstrates a medium that facilitates and records an electronic state change of embedded exotic molecules in ultra-cold chemistry, with sufficient sensitivity to constrain velocities of final-state particles.